1. Field of the Invention
The present invention relates to an improvement of an interchangeable magnetic head supporting mechanism for double-side type flexible disc drive apparatus.
2. Description of the Prior Arts
Among supporting mechanisms for this type apparatus already proposed, there is a supporting mechanism taking advantage of a two-directional flexibility of a window-frame shaped sheet spring as shown in FIGS. 1 through 4, and another supporting mechanism so designed as to push the rear surface of a magnetic head mounted on the sheet spring in contact with the center of the rear surface. Those mechanisms have not yet been matured to the mass production stage in their technical progress. The major reason for hindering the progress of the technology is of course that there has never been developed a mechanism with a good function to follow the surface of a memory medium of a head mechanism for supporting a magnetic head with pressure applied to both sides of a flexible disc. Because of a thin sheet made of polyethylene terephthalate as the disc, the rotation of the disc produces a vibrating wave in addition to a wavy motion inherently occurring with the disc rotation. The window-frame shaped directional plate spring as the supporting mechanism of the type in which a couple of heads are disposed above and below with respect to the disc, being slidably moved relative to the disc always in close contact with the disc, has the following inherent defects: (a) to be unduly sensitive to a wavy motion of the memory medium; (b) the deteriorated flatness of the plate spring member caused when the residual stress is released at the time of cutting it for shaping; (c) contracted deformation of the spring member caused when a flat cable (not shown) to provide a signal transfer to and from the magnetic head 1 is bonded to arms 5 and 5 of a support spring 2, as shown in FIGS. 1 through 4; (d) to apply an uneven pressure over the entire surface 10 of the sliding type magnetic head when it is in close contact with the medium, due to a difference between rigidities of the right and left portions of the member. There is an additional cause to facilitate the above-mentioned defects; when the magnetic head 1 is disposed with the flexible disc intervening therebetween, a line connecting the contacts on both sides of the head which are each made when the end 8 of the spring 7 pushes a projection 6 formed integrally on the support spring 2, hardly is orthogonal to the surface of the disc. Thus, the conventional supporting mechanism suffers from the manufacturing error from a static viewpoint and the defects caused by the wavy motion and the vibration of the medium from a dynamic viewpoint. Accordingly, an action line receiving the pressures from both the projections 6 and 6 can not be used for both the bifurcated head portions, so that the head poorly follows the disc. Incidentally, in FIGS. 1 to 4, reference numeral 3 designates a rectangular hole; 4 a head core; 9 a mounting base; 11 a mounting hole.
The idea of the above-mentioned supporting mechanism is exactly the same as that of a called floating mechanism used by a disc pack of aluminum alloy of a high speed rotatory type, for example. The alloy magnetic disc with high rigidity is free from an interaction of loads of the bifurcated portions of the head facing with each other when floating magnetic heads pushes both sides of the disc. This type magnetic head may be treated as a system of the mere combination of surface and a pressing projection on a thin air current layer, head floating surface. In other words, both the projections have not a common action line. Therefore, it is deemed to be erroneous to divert such an idea into the flexible disc under question.
To eliminate the above-mentioned defects, there has been proposed a mechanism as shown in FIGS. 5 and 6. In the figures, reference numeral 17 is a screw; 19 a turn arm; 25 a plate spring; 52 a gimbal spring; 55 an arm. The improved mechanism has a dull sensitivity to the wavy motion and the vibration, compared to the thin plate spring. Because of the presence of crossed two-fulcrums in its shape, the memory medium following characteristic is remarkably improved. However, when the moment applied by a sliding surface 10 of the magnetic head 1 is small, the crossed two-fulcrums must have somewhat enlarged widths. In this respect, this proposal still has some problem in the two-directional rotary following characteristic.